The present invention relates to a polishing apparatus for polishing a plate-like article such as a semiconductor wafer.
With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine, with spaces between wiring patterns also decreasing. As wiring spacing decreases to a level less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography and the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to have an exceptionally high degree of surface flatness.
FIG. 1 shows a conventional polishing apparatus for making the surface of a semiconductor wafer flat. The apparatus includes a turntable 101 provided with a polishing cloth 102 on the upper surface thereof, a wafer carrier 105 for carrying a semiconductor wafer 103 to be polished and an abrasive liquid supply nozzle 108 for supplying an abrasive liquid Q onto the polishing surface. The wafer carrier 105 is drivingly connected to a rotatable drive shaft 109 and is provided on its lower surface with a resilient backing member 107 formed from polyurethane or the like so that the semiconductor wafer 103 is supported on the backing member 107 with the entire upper surface of the semiconductor wafer engaged with the backing member 107.
Further, the wafer carrier 105 is provided therearound with a guide ring 106 to prevent the wafer 103 from becoming disengaged from the lower surface of the backing member 107. The guide ring 106 is fixedly secured to the wafer carrier with the lower surface of the guide ring 106 positioned at a lower level relative to the lower surface of the baking member 107, whereby the semiconductor wafer 103 is securely held under the lower surface of the backing member.
During a polishing operation, the wafer carrier 105 holds the wafer 103 on the lower surface of the backing member 107 and presses it against the polishing cloth 102 on the turntable 101 while the wafer carrier 105 and the turntable 101 are turned about their axes, respectively. Simultaneously, the abrasive liquid nozzle 108 supplies an abrasive liquid Q on the polishing cloth 102. The abrasive liquid consists of, for example, an alkaline slurry containing abrasive particles which chemically and mechanically polishes the semiconductor wafer by means of both the alkali and the abrasive particles.
Since, in such a conventional polishing apparatus, the semiconductor wafer 103 is engaged across its area with the backing member 107 when subjected to the polishing operation, the semiconductor wafer is readily affected by inconsistencies in the hardness of the backing member 107, thereby making it difficult for the semiconductor wafer 103 to be polished uniformly.
Further, since the polishing cloth provided on the turntable 101 is formed from a resilient member such as IC1000/SUBA400(IC1000 with 1,000 punched holes) produced by Rodel Nitta Corp., when the polishing cloth 102 is disengaged from the semiconductor wafer 103 the polishing cloth tends to rebound or spring back against the wafer, whereby an edge of the semiconductor wafer comes into engagement with a portion of the polishing cloth under a strong pressure, resulting, as shown in FIG. 2, in excessive polishing.
FIG. 3 is a graph showing the thickness A of an oxide layer of a 6 inch diameter semiconductor wafer polished by a conventional polishing apparatus, which thickness was measured at a number of points along a radius of the semiconductor wafer, and pressures B imposed on the semiconductor wafer at points on the radius during polishing of the semiconductor wafer. The values of the pressures were calculated through the so-called finite element method. It can be noted from the graph that the values denoting the pressures generally correspond to the values denoting the thickness of the oxide layer. It has been confirmed that a similar tendency exists with respect to a semiconductor wafer having an 8 inch diameter in terms of the above-stated oxide layer thickness and pressures.
Accordingly, it is an object of this invention to provide a polishing apparatus whereby a plate-like article such as a semiconductor wafer is polished to have a uniformly high degree of flatness.
According to the present invention, a polishing apparatus comprises a turntable having a flat surface, and a flat polishing pad provided on the flat surface of the turntable. The polishing pad has a polishing surface provided with grooves formed therein to divide the polishing surface into a number of sections. The apparatus further comprises an article carrier having an article holding surface for holding thereon a plate-like article having a surface to be polished. The carrier is adapted to press the surface of the plate-like article against the polishing surface of the polishing pad and to polish and flatten the surface of the plate-like article by relative movement between the article and the polishing surface. An annular member is positioned between the article holding surface and the plate-like article to form a chamber defined by the annular member, the article holding surface and the plate-like article, and a pressure control system is fluidly connected to the chamber for controlling pressure in the chamber. The annular member may be positioned along the peripheral edge of the plate-like article. The grooves may be arranged in a grid-like pattern.
The plate-like article is pressed against the polishing surface under a pressure exerted by the pressurized fluid while pressing the plate-like article against the polishing surface through the annular member.
The annular member may have a width in a range of from 10 mm to 20 mm. According to another aspect of the present invention, a polishing apparatus comprises a turntable having a surface, and a polishing pad provided on the surface of the turntable. The polishing pad has a polishing surface. The apparatus further comprises an article carrier having an article holding surface for holding thereon a plate-like article having a surface to be polished. The carrier is adapted to press the surface of the plate-like article against the polishing surface of the polishing pad and to polish and flatten the surface of the plate-like article by relative movement between the article and the polishing surface. An annular member is positioned between the article holding surface and the plate-like article to form a chamber defined by the annular member, the article holding surface and the plate-like article. The annular member has a width in the range of from 10 mm to 20 mm, and a pressure control system is fluidly connected to the chamber for controlling the pressure in the chamber. The annular member may be positioned along the peripheral edge of the plate-like article.
According to a further aspect of this invention, a polishing apparatus comprises a turntable having a surface, and a polishing pad provided on the flat surface of the turntable. The polishing pad has a polishing surface. The apparatus further comprises an article carrier having an article holding surface for holding thereon a plate-like article having a surface to be polished. The carrier is adapted to press the surface of the plate-like article against the polishing surface of the polishing pad and to polish and flatten the surface of the plate-like article by relative movement between the article and the polishing surface. An outer member in the shape of a ring is placed between the article holding surface and the plate-like article to form a chamber defined by the outer member, the article holding surface and the plate-like article, and an inner member is positioned inwardly of the outer member between the article holding surface and the plate-like article to divide the chamber into a plurality of chamber sections separated from each other. The polishing apparatus may further includes a pressure control system fluidly connected to the chamber for controlling pressures in the chamber sections. The outer member may be positioned along the peripheral edge of the plate-like article.
The inner member may be in the form of a ring and positioned coaxially with the outer member to divide the chamber into outer and inner chamber sections. The pressure control system may include regulators for controlling the pressures in the inner and outer chamber sections such that a pressure in the inner chamber is made greater than that in the outer chamber.
It is preferable that for the outer member is to have a width which is greater than that of the inner member. Further, it is preferable for a ratio of the pressure in the inner chamber section to the pressure in the outer chamber to be set to be 1:0.5-1:0.8. The outer and inner members may be formed from a non-permeable material such as silicon rubber, polyethylene terephthalate, polyurethane, polyethylene and resist film.
In accordance with a further aspect of the present invention, there is provided a polishing apparatus comprising a turntable having a surface, a polishing pad provided on the surface of the turntable, an article carrier having an article holding surface for holding thereon a plate-like article having a surface to be polished, and a backing member positioned between the article holding surface and the plate-like article to form a space between the holding surface and the plate-like article. The member is formed from a polyethylene terephthalate sheet.
These and other features and advantages of the present invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings wherein like reference numerals designate like or corresponding elements throughout the several views.